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Description  |
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DESCRIPTION OF THE INVENTION
From one aspect, the present invention relates to apparatus for casing
metal by uphill teeming. The invention also relates to a method of
casting, to a tubular assembly for use in the apparatus and to a method of
preparing the assembly.
Uphill teeming is used for casting ingots from molten metal. For casting in
this way, a plurality of vertically extending moulds are interconnected by
a series of horizontal passageways defined by runners, which passageways
communicate with the bottom ends of the moulds and also communicate with
the bottom end of a tubular guide assembly. The guide assembly extends
upwardly from the runners to a height at least equal to that of the
moulds. Molten metal is discharged from a ladle or other container into
the guide assembly and flows therefrom into the moulds. The metal is then
permitted to solidify in the guide assembly, runners and moulds and,
subsequently, the moulds are stripped from the cast ingots.
Known guide assemblies and runners used in uphill teeming comprise a
plurality of ceramic tubes arranged end-to-end. The individual ceramic
tubes generally have a length in the range 130 to 450 millimeters. It is
considered unsatisfactory to make longer ceramic tubes. Since the guide
assemblies and runners commonly have lengths exceeding one meter and often
exceeding two meters, it is necessary for a plurality of ceramic tubes to
be used in each runner and in each guide assembly.
The ceramic tubes are supplied to a steel works where they are assembled
into the required runners and guide assemblies. The preparation of runner
and guide assemblies from separate ceramic tubes requires a considerable
amount of labour and, in the case of guide assemblies, extensive use of
cranes. The preparation of guide assemblies and runner is one factor
limiting the rate of production of cast ingots in steel works.
According to one aspect of the present invention, there is provided an
assembly comprising an inner refractory tube and an outer structure which
embraces the inner tube. The assembly may be a guide assembly, by which we
mean herein an elongated assembly used in uphill teeming and through which
molten metal is poured towards a plurality of runners, or the assembly may
be a runner assembly, by which we mean herein an assembly of elements
which is used in uphill teeming as or as the main part of a runner for
conveying molten metal away from the guide assembly towards a mould.
An assembly in accordance with the invention can be handled more
conveniently than can separate ceramic tubes and the time required for the
preparation in the steel works of apparatus for uphill teeming is reduced
by use of assemblies in accordance with the first aspect of the invention.
Known guide assemblies further comprise a hollow metal casing in which the
ceramic tubes are disposed. In some cases, the ceramic tubes are a close
fit inside the casing so that the ceramic tubes are supported directly by
the metal casing. It is also known to provide a metal casing having
internal dimensions substantially greater than the external dimensions of
the ceramic tubes to provide an inter-space which is packed with sand or
other refractory material to support the ceramic tubes. In this case, the
metal casing supports the ceramic tubes indirectly via the packing. The
packing is poured into the metal casing but the discreet particles or
pieces of the packing are free to fall away from each other when the
casing is opened.
After a casting operation has been performed by uphill teeming, the
solidified metal remaining in the guide assembly and the metal casing of
the guide assembly are recovered for further use. To this end, known
casings are assembled from components which abut each other in parting
planes containing a longitudinal axis of the guide assembly. No component
of the guide assembly extends continuously completely around the axis so
that each component of the casing can be moved away from the ceramic tubes
in a direction transversely of the axis.
According to a further aspect of the invention, there is provided a guide
assembly of tubular form comprising an inner tube of refractory material
and an outer tube which is continuous around a longitudinal axis of thwe
assembly. Because the outer tube of an assembly in accordance with the
second aspect of the invention does not include joints between components
which abut in a parting plane containing the axis of the assembly, the
outer tube can be less massive than are the casings of known guide
assemblies.
In an assembly in accordance with the first aspect of the invention, the
outer structure preferably comprises a coherent mass of particulate
material embracing the external surface of the inner tube. By the
description "coherent", we mean that the particles are bound ot each
other, as distinct from the loose fill used heretofore. For binding the
particles together there may be used a binder which is used for binding
particles of sand or other aggregate in foundry moulds or cores. These
binders are applied to the particles in an uncured condition such that the
coated particles are capable of flowing or being packed together to form a
body of predetermined shape. The binder is then cured to form a rigid,
coherent body of the required shape. When subjected to a high temperature,
the binder may be degraded so that after used the coherent mass can be
disrupted.
The preferred assembly embodies both the first and second aspects of the
invention, having an outer tube which contains the coherent mass of
particulate material and is continuous around a longitudinal axis of the
inner tube. The outer tube is preferably formed of a material which is
softer than, this is has a lower hardness than, mild steel.
The material of which the outer tube is formed may advantageously be
destructable. The outer tube may have a character such that it is
inevitably destroyed in consequence of the pouring of a batch of molten
steel through the inner tube of the assembly. Alternatively, the outer
tube may be characterised in that, at least after use of the assembly to
convey a batch of molten steel, the outer tube can be disrupted without
cutting (for example shattered by impact) to expose and to facilitate
disruption of the inner tube.
The outer tube may have a character such that, before use of the assembly
to convey molten steel, the outer tube can be disrupted without cutting,
for example by impact, but it is a preferred characteristic of the other
tube that flow of molten steel through the assembly reduces the strength
of the outer tube and renders the outer tube more fragile or substantially
destroys the outer tube. The material of which the outer tube is formed
may be combustible or degradable by heating to a temperature within the
range 300.degree. to 600.degree. C. For convenience, we refer hereinafter
to a material having this characteristic as being non-refractory.
The outer structure of the assembly is preferably adapted to act as a heat
sink. By this, we mean that the outer structure is formed of or includes a
material which is a good conductor of heat, for example a better conductor
than silica sand, and preferably has a high specific heat, for example
higher than that of silica sand. Olivine is a suitable particulate
material. Serpentine also may be used.
The inner tube of the assembly may comprise a plurality of pre-formed
tubular elements of refractory material arranged end-to-end to form a row.
The tubular elements may be ceramic tubes as used in known guide
assemblies and runners. Alternatively, the inner tube may be formed of
other refractory material, for example a coherent mass of particulate
material. The inner tube may be formed of silicate-bonded silica sand. The
inner tube may comprise a single coherent body of bonded particulate
material or one relatively long tubular element with a shorter tubular
element at one or each of its ends.
The outer structure may be a holding structure which extends along a row of
pre-formed tubular elements constituting the inner tube, the holding
structure being secured to at least a pair of the tubular elements
disposed at opposite ends of the inner tube to hold the tubular elements
against longitudinal movement away from each other.
Preferably, the holding structure is stressed in tension and the inner tube
is stressed in compression. Relative movement of the holding structure and
inner tube longitudinally of the inner tube may be prevented solely by
friction between the elements of the inner tube and the holding structure.
The holding structure may include clamping means for establishing
sufficent friction between the holding structure and the elements of the
inner tube.
The holding structure preferably comprises one or more elongate elements,
the or each of which overlaps with all elements of the inner tube, and
clamping means for clamping the or each elongate element to at least
elements of the inner tube disposed at opposite ends of the row. There may
be a single elongate element of tubular form, through which the inner tube
extends.
The elongate element or elements of the holding structure is or are
preferably thin, as compared with the inner tube, that is to say the
volume of the or each elongate element is small, as compared with the
volume of the inner tube.
Suitable materials for the elongate element of an assembly or for at least
one elongate element of an assembly having more than one elongate element
include compacted fibrous materials, for example cardboard. Thus, the
assembly may comprise a row of ceramic tubes embraced by a cardboard tube
which is clamped to at least the ceramic tubes at the end of the row.
Alternatively, the or each elongate element may be formed of metal or a
plastics material and either be flat or have a cross-section including one
or more angles, preferably right angles.
According to a further aspect of the invention, there is provided apparatus
for casting metal by uphill teeming and comprising a plurality of
vertically extending moulds, a vertically extending guide assembly of
tubular form and a plurality of runner assemblies defining respective
passageways which communicate with the bottoms of the moulds and which the
bottom of the guide assembly, wherein at least one of said assemblies is
in accordance with the first aspect of the invention.
According to a further aspect of the invention there is provided a method
of preparing a guide assembly or a runner assembly for use in uphill
teeming wherein a plurality of ceramic tubes are arranged end-to-end to
form a row and at least tubes at opposite ends of the row are secured to a
holding structure which extends along the row to hold the tubes against
longitudinal movement away from each other.
According to a still further aspect of the invention there is provided a
method of casting metal by uphill teeming wherein a plurality of ceramic
tubes are assemblied in end-to-end relation and are held in said relation
by means of a holding structure, further assemblies of tubes and holding
structure are prepared in the same manner, the assemblies are transported
to the site at which the metal is to be cast, a vertically extending guide
assembly of tubular form is erected at said site, a plurality of runner
assemblies of tubular form are arranged to radiate from the bottom end of
the guide assembly to provide substantially horizontal passageways
communicating with the interior of the guide assembly, a plurality of
moulds is arranged around, but spaced from, the guide assembly with each
mould communicating at its bottom with a passageway defined by a
respective runner assembly, the assemblies of ceramic tubes and holding
structures being used as the runner assemblies and, optionally, the guide
assembly, metal is poured into an upper end of the guide assembly to flow
down the guide assembly and through the runner assemblies into the moulds
and the metal is permitted to solidify in the moulds, runner assemblies
and guide assembly.
There is also provided in accordance with the invention a method of
preparing a guide assembly wherein a plurality of tubular elements of
ceramic material are arranged end-to-end inside an outer tube with an
annular spaced between the internal surface of the outer tube and the
external surfaces of the elements, particles of a refractory material are
coated with a curable binder, the annular space is packed with the coated
particles and the binder is cured.
The invention also provides a method of casting metal wherein a guide
assembly including an outer tube of non-refractory material is prepared by
the method hereinbefore defined, molten metal is guided by means including
the guide assembly from a source to a mould, the metal solidifies in the
guide assembly and in the mould, the outer tube burns and/or is degraded
by heat which penetrates through the packing of refractory particles from
the metal within the guide assembly and, after the metal in the guide
assembly has solidified, the mass of refractory particles is disrupted to
expose the elements of ceramic material.
Examples of assemblies, apparatus and methods embodying the invention will
now be described, with reference to the accompanying drawings, wherein:
FIG. 1 shows diagrammatically the general arrangement of apparatus for
uphill teeming, top and bottom plates thereof being partly broken away;
FIG. 2 shows in side elevation and on enlarged scale a runner assembly of
the apparatus shown in FIG. 1;
FIG. 3 shows an end view of the runner assembly of FIG. 2;
FIG. 4 shows an end view of a first alternative runner assembly;
FIG. 5 shows an end view of a second alternative runner assembly;
FIG. 6 shows a fragmentary cross-section in a vertical plane of an
alternative guide assembly which may be used in the apparatus of FIG. 1;
and
FIG. 7 shows a cross-section similar to that of FIG. 6 of a further
alternative guide assembly.
The apparatus illustrated in FIG. 1 includes a bottom plate 10 in the upper
face of which there is formed a number of channels radiating from the
centre of the face. Each channel contains a runner assembly 11 and the
runner assemblies are covered by an upper plate 12 which rests on the
lower plate. Sand or other particulate, refractory material may be brushed
into the channels after the runner assemblies have been placed therein in
order to fill the channels and ensure that the top plate holds the runner
assemblies firmly in their respective channels.
At the outer end of each runner assembly 11 there is a riser 13 which
extends upwardly through an aperture in the top plate and communicates
with the bottom end of a corresponding mould 14 which stands on the top
plate. In the particular example illustrated, the number of moulds 14 is
equal to the number of runner assemblies 11. Alternatively, some of or
each of the runner assemblies may be provided with a riser intermediate
its ends, in addition to the riser at its end, there being associated with
each such runner assembly two moulds.
At the centre of the group of moulds 14 there extends upwardly from the
plates 10 and 12 a guide assembly 15 which is of tubular form. An upper
end of the guide assembly is at approximately the same level as the upper
ends of the moulds 14. At its lower end, the guide assembly rests on a
centre block 16 formed with passageways which provide communication
between the interior of the guide assembly 15 and the interiors of the
hollow runner assemblies 11.
The runner assemblies 11 are similar to one another except with respect to
length and one of these is illustrated in FIGS. 2 and 3. The runner
assembly shown in FIG. 2 comprises an inner tube which consists of a
plurality of tubes of which there are four in the example illustrated. The
tubes are formed of ceramic or other refractory material. These tubes, 17
to 20, are arranged end-to-end to form a rectilinear row and are held in
this relation with one another by a holding structure. The holding
structure comprises a plurality of elongate elements which extend along
the row from a position near to one end thereof to a position near to the
opposite end. The tubes 17 and 20 at the ends of the row project somewhat
beyond the elongate elements of the holding structure.
A first elongate element of the holding structure is in the form of a tube
21 which extends continuously around an axis 22 of the runner assembly and
overlaps with all of the ceramic tubes. The holding structure further
includes elongate elements 23 and 24 of angle section which are interposed
between the tube 21 and the tubes 17 to 20.
The tube 21 and angle sections 23 and 24 are secured in pressure contact
with the tubes 17 and 20 by clamping means comprising metal bands 25 and
26 which embrace the tube 21 near to its ends. In consequence of the
pressure contact established and maintained by the bands 25 and 26, there
is sufficient friction between the tubes 17 and 20 on the one hand and the
tube 21 and angle sections 23 and 24 on the other hand to prevent movement
of the tubes 17 and 20 relative to the tube 21.
During application of the bands 25 and 26, the ceramic tubes 17 to 20 are
subjected to a force along the axis 22 which stresses the ceramic tubes in
compression. When the bands have been applied, this compressive stress is
at least partly maintained by the tube 21 and the angle sections 23 and
24. Additionally, during application of the bands 25 and 26, the angle
sections 23 and 24 and/or the tube 21 may be subjected to tensile stress.
Opposite ends of each of the bands 25 and 26 are secured together in any
known manner. If required, the holding structure may include means for
tightening the bands 25 and 26. Additional bands may be provided on those
parts of the tube 21 which embrace the cermic tubes 18 and 19.
The runner assembly of FIGS. 2 and 3 is portable, by which we mean it can
be moved on its own. The assembly is prepared, possibly on a mandrel,
before being transported to the site where it is to be used. The mandrel
may be retained in the assembly until the latter is placed in the bottom
plate 10.
In plate of the row of tubes 17 to 20, there may be provided an inner tube
which consists of a single integral body of refractory material. The
single inner tube may be formed by extrusion of silica sand coated with
silicate binder, the binder being cured in a known manner after extrusion
of the mixture. The outer tube 21 and the angle section elongate elements
23 and 24 would then be held in pressure contact with the single inner
tube adjacent to opposite ends thereof by the metal bands 25 and 26. The
holding structure would protect the inner tube against subjection to
longitudinal tensile stress. To this end, the single inner tube may be
stressed in compression whilst the holding structure is stressed in
tension.
In the particular example illustrated in FIG. 3, the ceramic tubes 17 to 20
have a square profile, as viewed in cross-section, and a cylindrical bore.
The cross-section of the elements 23 and 24 includes a right angle. These
elements are fitted on opposite corners of the ceramic tubes. The tube 21
has a square cross-section corresponding to the profile of the ceramic
tubes.
As illustrated in FIG. 4, the outer tube 21 may be omitted. The bands 25
and 26 then embrace the angle sections 23 and 24 and the tubes 17 and 20.
Alternatively, the angle sections 23 and 24 may be omitted from the
arrangement shown in FIG. 3. Either of these omissions may also be made in
the case where the inner tube is a single integral body.
In either the assembly illustrated in FIG. 3 or the alternative assembly
illustrated in FIG. 4, there may be substituted for the angle sections 23
and 24 flat strips which overlie flat surfaces of the ceramic tubes 17 to
20 or a single channel-section element in which the ceramic tubes are
received.
The angle section elements 23 and 24 may be formed of metal or of a
plastics material. The material of which these elements are formed is
thin, as compared with the thickness of the walls of the inner tube. The
thickness of the material of which the elements 23 and 24 are formed
preferably does not exceed one tenth the wall thickness of the inner tube
and may be approximately one thirtieth of this wall thickness.
The wall thickness of the tube 21 also is less than the minimum wall
thickness of the inner tube. The wall thickness of the tube 21 is
approximately one seventh the minimum wall thickness of the ceramic tubes
17 to 20 in the example illustrated but is exaggerated in FIG. 3. In
general, this wall thickness is preferably less than one third of the
minimum wall thickness of the inner tube. Also the wall thickness of tube
21 does not exceed one tenth of and may be less than one thirtieth of the
mean external cross-sectional dimension of the inner tube.
The tubular elongate element 21 is preferably formed of a material
comprising a compacted mass of fibres, for example cellulose fibres.
Cardboard is a suitable material. This results in a holding structure
which is considerably less massive than the inner tube. Alternatively, the
fibres may be inorganic, for example glass or mineral fibres.
At least one and possibly all of the elongate elements may be formed of a
material which is combustible or degradable by heating to a temperature
within the range 300.degree. to 600.degree. C. At least one of the
elongate elements is preferably formed of a material which is softer than
mild steel. The angle sections 23 and 24 may be formed of mild steel.
In the example of runner assembly illustrated in FIG. 5, the inner tube 120
has a circular profile, as viewed in cross-section, but in other respects
is in one of the forms described with reference to FIG. 3, and the holding
structure comprises a pair of angle section elements 123, 124 which extend
along the inner tube and are secured thereto by bands 126 which embrace
the inner tube and the angle section elements. If required, the assembly
illustrated in FIG. 5 may further comprise a cylindrical tube of cardboard
arranged in a similar manner to the tube 21 of FIG. 3.
Whatever materials are used for the elongate elements of the holding
structure, at least one of these elements is preferably formed of a
material having a higher tensile strength than do the ceramic tubes 17 to
20.
The guide assembly 15 shown in FIG. 1 also comprises an inner tube of
refractory material and an outer structure which embraces the inner tube.
The inner tube may be one of the forms hereinbefore described in
connection with the runner assemblies 11. The outer structure may be a
holding structure in one of the forms hereinbefore described. The guide
assembly has a length within the range two to three meters and an outside
diameter, over the major part of its length, a little greater than 200
millimeters. The inner tube defines a cylindrical passageway extending
along an axis 30 of the guide assembly and having a diameter of
approximately 100 millimeters.
The guide assembly comprises a further hollow element 31 having a flared
upper end portion which tapers downwardly and merges with a lower end
portion (not shown) disposed within the outer structure of the guide
assembly and communicating with the inner tube.
One particular guide assembly for use in the apparatus of FIG. 1 is
illustrated in FIG. 6. In this guide assembly, the inner tube comprises a
plurality of ceramic tubular elements 32 which are connected end-to-end by
spigot and socket joints which, when the spigots are properly inserted in
the sockets are substantially metal-tight. A lower one, 32a, of the
elements 32 includes a lower end portion which projects slightly beyond
the outer structure to fit over a spigot on the centre block 16.
Alternatively, the end portion could be downwardly tapered adjacent to its
free end to engage in a socket provided in the centre block 16. Each
element 32 has a length which exceeds its largest transverse dimension.
The outer structure of the guide assembly shown in FIG. 6 comprises an
outer tube 33 and an intermediate body 34 disposed between the inner and
outer tubes. The outer tube embraces the intermediate body and the
intermediate body embraces the inner tube.
The intermediate body 34 is a heat sink. This body is formed of particles
of olivine or other magnesia-containing material, by which we mean a
material containing chemically combined magnesium and oxygen, which are
bound into a coherent mass by a binder, typically a binder used in the
foundry industry for binding particules of aggregate in cores and moulds.
A silicate binder may be used.
Both the outer tube 33 and the intermediate body 34 are continuous around
the axis 30 and both of these are destructable, by which we mean herein
that, at least after use of the guide assembly, the outer tube and
intermediate body can be disrupted without cutting. In the particular
example illustrated in FIG. 6, the outer tube is of non-refractory
material. The preferred non-refractory material is cardboard. An outer
tube of cardboard preferably has a wall thickness in the range 9 to 24
millimeters.
An upper end portion of the outer tube 33 is embraced by or, as shown in
FIG. 6, embraces a cylindrical part of a funnel 35 (not shown in FIG. 1).
The funnel may be clamped on the outer tube or be an interference fit
thereon. As shown, the intermediate body 34 of olivine extends between the
upper part of the funnel 35 and the flared part of the inner element 31 so
that, acting via the olivine body, the funnel supports the flared end
portion of the element 31.
The guide assembly further comprises suspension means for co-operating with
lifting tackle. The suspension means illustrated in FIG. 6 comprises a
releasable clamp 27 which embraces the cylindrical part of the funnel 35
and overlapped part of the outer tube 33 and clamps these to each other.
The clamp has eyes or rings to receive hooks or the like of lifting tackle
(not shown), whereby the guide assembly can be suspended with its axis 30
substantially vertical. As shown in FIG. 1, the suspension means further
includes bars 38 attached to the clamp 37 and engageable with the moulds
14 to provide location for an upper part of the guide assembly when the
guide assembly is positioned at the centre of the top plate 12.
A lower end portion of the outer tube 33 is embraced by a sleeve 39 formed
of material harder than, and having greater strength than, cardboard,
preferably mild steel. As shown in FIG. 6, there may be provided on the
lower end of the sleeve 39 a flange 40 which rests on a shoulder provided
on the lower elements 32a of the inner tube. The lower end of the outer
tube 33 then rests on the flange 40. The length of the sleeve 39 is such
that it embraces the entire part of the outer tube which is disposed
within a well of the top plate 12 in use.
After the guide assembly of FIG. 6 has been placed on the centre block 16
and the well in the top plate has been filled up with refractory material,
wedges are driven into the well to engage between the top plate and the
sleeve 39. The sleeve protects the outer tube 33 from abrasion by the
wedges and distributes the pressure exerted on the sleeve by the wedges.
An alternative form of suspension means (not shown) which may be provided
in the guide assembly of FIG. 6 comprises a plurality of known cavity
fixing devices which are inserted through apertures formed in the outer
tube 33 prior to packing of the space between the outer tube and the inner
tube with particulate material. The assembly can then be suspended from
lifting gear by means of the cavity fixing devices. In a case where the
outer structure of the guide assembly includes elongate elements,
additional to the outer tube and having a tensile strength greater than
that of the cardboard of which the outer tube is formed, the elongate
elements may be secured at their lower ends to the sleeve 39 and at their
upper ends either to the funnel 35 or to the clamp 37.
In a modification of the guide assembly shown in FIG. 6, the sleeve 39 may
be omitted. The outer tube 33 may then extend almost to the free end face
of the lower element 32a of the inner tube. The intermediate body 34 may
be exposed adjacent to the free end of the element 32a or that element may
have a radially outwardly projecting flange which closes the lower end of
the space between the inner and outer tubes. The width of this space, that
is the wall thickness of the intermediate body 34, is typically 30
millimeters.
The guide assembly illustrated in FIG. 6 is prepared by fitting the
elements 32 of the inner tube around a mandrel, placing the outer tube 33
about the inner tube, then adding the flared element 31 to the inner tube
and pouring, blowing or ramming particles of olivine which have been
coated previously with a curable binder into the space between the inner
and outer tubes. The binder is then cured.
In a case where curing is effected by passing a gaseous curing agent into
the mass of particulate material, a plurality of holes may be formed in
the outer tube 33 to admit the curing agent. The funnel 35 and clamp 37
may be fitted either before or after the particulate material is poured
into the annular space between the inner and outer tubes.
The completed guide assembly is portable and is transported from the site
at which it is prepared to the site at which metal is to be cast and is
there assembled with the other parts of the apparatus shown in FIG. 1. The
mandrel may be removed from the guide assembly prior to transporting the
guide assembly or may remain within the inner tube until the guide
assembly has been placed on the block 16 and connected to the moulds 14.
When a batch of molten steel is poured through the guide assembly and the
runners 11 into the moulds 14, heat flows through the wall of the inner
tube and through the intermediate body 35 to the outer tube 33. This
causes degradation of the outer tube or, in a case where the outer tube is
formed of cardboard or other combustible material, combustion of the outer
tube. By the time the moulds have been filled and the steel solidifies in
the guide assembly, runners and moulds, a cardboard outer tube has been
substantially destroyed. The binder of the intermediate body 34 also may
have been degraded so that the remains of the outer tube and the
intermediate body can readily be disrupted by impact, access can be gained
to the inner tube 33 and this can then be disrupted by impact to
facilitate recovery of the solidified steel from within the guide
assembly. Each runner assembly is similarly destroyed to facilitate
recovery of the steel which has solidified in the runners.
In FIG. 7, there is illustrated a further example of a guide assembly which
may be used in the apparatus of FIG. 1. Certain parts of the guide
assembly shown in FIG. 7 correspond to parts hereinbefore described with
reference to FIG. 6 and such corresponding parts are identified in FIG. 7
by like reference numerals with the prefix 1. Except for the differences
hereinafter mentioned, the preceding description is deemed to apply to
such corresponding parts.
The guide assembly of FIG. 7 differs from that of FIG. 6 primarily in the
character of the outer tube 133. This outer tube is formed of a
non-metallic material which is capable of withstanding without significant
combustion or degradating the rise in temperature which is caused by the
pouring of a batch of molten steel through the inner tube of the assembly.
The material is, however, preferably destructable, that is capable of
being disrupted without cutting both before and after use of the guide
assembly. The outer tube 133 is formed of a material which is initially in
a flowable or mouldable condition and is set after being formed to the
required shape. The outer tube may be formed by casting or extruding
material prior to assembly of the outer tube with the inner tube.
Alternatively, the material of which the outer tube is formed may be
applied to the intermediate body 134 after the intermediate body and inner
tube 133 have been assembled together. The outer tube may be extruded or
sprayed onto the intermediate body. Alternatively, the intermediate body
134 may be omitted, the outer tube 133 being applied directly to the inner
tube. The outer tube may be formed of or formed mainly of a castable
refractory material or other cementitious material.
In a modification of the guide assembly shown in FIG. 7, the outer tube 133
may incorporate filamentary reinforcing material, for example metal wires
or inorganic fibrous material. Glass fibre or ceramic fibre may be used.
The reinforcement may be incorporated in cementitious material prior to
forming of the latter into the outer tube or the reinforcement may be
applied to the inner tube or to the intermediate body and cementitious
material then applied to provide a matrix in which the reinforcement is
embedded.
Inorganic fibrous material may also be used in a modification of the guide
assembly shown in FIG. 6, in place of the cardboard or other organic
fibrous material. In this case, the outer tube is formed of or is formed
partly of mineral fibre or glass fibre. A pre-formed outer tube comprising
mineral fibre or glass fibre may be fitted over the inner tube and the
intermediate body then formed between the inner and outer tubes.
Alternatively, the intermediate body may be formed about the inner tube
and a cloth or tape comprising glass or mineral fibre then wrapped or
otherwise applied around the intermediate body. The glass or mineral
fibres may be bonded together after being applied around the intermediate
body by a binder which is degraded by heat during use of the guide
assembly.
Whilst we prefer to provide an outer tube which is destructable, an
assembly in accordance with the invention may incorporate a reusable outer
tube, for example an outer tube formed of mild steel. In this case, it is
necessary to remove the outer tube from other parts of the assembly after
use and before the solidified steel within the assembly can be recoverd.
Steel and each of the other materials mentioned hereinbefore as being
suitable for the outer tube of a guide assembly may also be used to form
the outer tube of a runner assembly in accordance with the invention. The
runner assemblies may be prepared in the same manner as the guide
assemblies and transported to the site at which steel is to be cast,
mandrels optionally being present in the runner assemblies during
transport to contribute to the strength of the assemblies.
There may be provided between the inner and outer tubes of a runner
assembly as hereinbefore described an intermediate body which is a heat
sink and may be as herein described with reference to the guide
assemblies. If, during a casting operation, there is a leakage of molten
steel through the wall of the inner tube of either a guide assembly or a
runner assembly, for example through a crack in a tubular element of the
assembly or through a joint between adjacent tubular elements, the molten
steel which emerges from the inner tube will contact the intermediate body
and will be chilled thereby. In this way, the steel will be frozen and
will seal the crack or joint to prevent further leakage. In order that any
such leakage should be terminated without molten steel pentrating to the
outside of the assembly, it is important that the intermediate body should
not act as a thermal insulator but should rapidly conduct heat away from
the penetrating steel. A high specific heat of the material of which the
intermediate body is formed also assists rapid freezing of the steel.
Whilst we prefer that the intermediate body comprises a coherent mass of
particulate material, the intermediate body may comprise a mass of
particules which are not bound to each other. In this case, the annular
space between the inner and outer tubes of an assembly may be closed at
opposite ends of the assembly by annular elements which may be formed of
the same material as the outer tube. As in the case of known guide
assemblies, the inner tube of each assembly herein described is formed of
a material which is a thermal insulator, relative to the intermediate
body, in order to reduce the loss of heat from the molten steel which
flows through the assembly.
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